(1) Field of the Invention
This invention relates to a surface mount technology type coaxial connector, for instance, ultra miniature high frequency coaxial connector that connects a coaxial cable with a substrate and is used in such high frequency communication equipment as portable phone and automobile telephone.
(2) Description of the Prior Art
Conventionally this type of surface-mounted coaxial connector was composed as described in the Provisional Publication No. 6755-1993 laid open Jan. 29, 1993. In this prior art the coaxial connector comprises a plug 11 connected to one end of a coaxial cable and a receptacle 13 surface-mounted on a substrate (for example, on a printed circuit board) as shown in FIG. 1, and the coaxial cable 10 and substrate 12 are electrically connected by fitting the plug 11 into the receptacle 13.
As shown in FIG. 2, the plug 11 is provided with a laterally L-shaped insulator 14 whose top is formed into a cylindrical fitting portion 15 at the center of which is mounted a central contact 16 made from a female type contact. The conductor crimp portion 17 of this central contact 16 crimp the central conductor 18 of the coaxial cable 10. The term "crimp" in this and later contexts means that members are fastened together under certain pressure so as not to separate them. The coaxial cable 10 is covered outside the central conductor 18 sequentially with a cylindrical insulator 19, a braid 20 as shielded conductor and casing 27.
The insulator 14 is covered with the shield cover 22 that is a shielding member, the top portion of which is formed into a cylindrical shell 23. An annular insertion 24 is constructed between the shell 23 and the fitting portion 15 of the insulator 14. On the bottom portion of the shield cover 22, formed sequentially are the insulator crimp portion 25 crimped into the outer portion of the braid 20 of the coaxial cable 10, and the casing crimp portion crimped into the outside portion of the casing 27 of the coaxial cable 10.
The receptacle 13 that is composed of the insulator 29, shell 30 and the central contact 31 as shown in FIG. 3 (a), (b), and (c) is assembled as follows. As shown in FIG. 4, the shell 30 is inserted from the upper part of the insulator 29, the cylindrical shell 32 of the shell 30 is fitted into the outer circumference of the projection formed at the center of the concave depression 33 of the insulator 29 while press-fitting the terminals 35, 35 and 35 into ports 36, 36, and 36 to be projected on the lower face, and these terminals 35, 35, and 35 thus projected are folded outward into the notches 37, 37, and 37 to form the grounding terminals. In this text, the term "fitting" means fitting two objects into each other, and the term "press-fit" means putting something into another thing pressing it against some pressure.
On the other hand the central contact 31 is inserted from the lower portion of the insulator 29, the contact portion 38 of the central contact is inserted into the contact insertion bore 39 of the insulator 29, and the leg 40 of the central contact is inserted into the groove 41 of the insulator 29 to form the hot terminal.
Then, as shown in FIG. 5, the receptacle 13 is automatically mounted on the substrate 12 by means of the adsorption nozzle of an automatic mounting machine. Then, by fitting into the shell 32 of the receptacle 13 the shell 23 of the plug 11 shown in FIG. 2, the central contact 16 and shell 23 of the plug 11 fit into and contact the central contact 31 and shell 32 of the receptacle 13, connecting thus the coaxial cable 10 electrically with the substrate 12.
In another example of prior art, there existed a sleeve 21 inserted between the cylindrical insulator 19 and the braid 20 outside the cylindrical insulator 19 in the coaxial cable 10 as shown in FIG. 6. This sleeve 21 is made of, for instance, from phosphor bronze so as to endow it with conductivity. In FIG. 6 the numeral 59 symbolizes that locking spring mounted outside the shell 23 which reinforces the elasticity of the shell 23. Other configurations being nearly the same with those shown in FIG. 2, explanation will be omitted with like numerals representing the like portions for short.
The surface mount type coaxial connector in the prior art was however problematical in that, the central contact 16 of the plug 11 being made from a female contact having a slit intended to give some plasticity, the central contact 16 of the plug 11 was too long and consequently the height Hp of the shield cover 22 was too large, making thus it difficult to save space.
Another problematical point was that the length Lp was too large (for example, Lp=7 mm) from the center line 43 to the bottom end of the shield cover 22 due to the conductor crimp portion 17 of the central contact 16 in the plug 11 that was formed on the coaxial cable 10 from the center line 43 and to the casing crimp portion 28 that was provided besides the braid crimp portion 26. Space-saving was difficult in this case too.
Though it is conceivable to reduce the length Lp by omitting one of the two: the braid crimp portion 26 and the casing crimp portion 28, this omission would weaken the crimp force between the shield cover 22 and the coaxial cable 10 in the plug 11 because of the level difference between the braid 20 and the casing 27 in the coaxial cable 10.
On the other hand, the assembling workability is worse, because the direction of incorporation is reversed of the shell body 30 and central contact 31 to be press-fitted and fixed onto the insulator 29 as shown in FIG. 4, and consequently the terminals 35, 35, and 35 are folded outward after the press-fitting of the shell body 30 into the insulator 29.
Since further the top face on the plug fitting side of the insulator 29 in the receptacle 13 was designed to be situated inward (that is, on the side of the substrate 12) from the top face on the plug fitting side of the shell body 30, the dimension of the adsorption nozzle 42 of the automatic mounting machine was limited, thereby reducing the degree of freedom in designing the nozzle, lessening the contact area with the nozzle 42 and worsening the adsorption stability under high-speed mounting.
The adsorption nozzle is subjected to a large dimensional restriction, because, as shown in FIG. 5, the outer diameter G of the adsorption nozzle 42 should be larger than the inner diameter D of the shell body 30 (G&gt;D) and that the inner diameter N of the nozzle 42, namely the inner diameter N of the inlet port should be equal to or less than the outer diameter C of the shell body 30 (N.ltoreq.C). Since, moreover, the contact is only between the top face of the shell 30 and the top face of the adsorption nozzle 42, the contact area for adsorption becomes necessarily smaller.
As is shown by the dotted line in FIG. 5, some prior art makes airtight the adsorption cover 44 outside the shell body 30 or bonds an adsorption tape on the shell body 30 in order to enlarge the adsorption area with the adsorption nozzle 42. These adoptions however worsen the assembling workability because additional work is required to remove the adsorption cover 44 and the adsorption tape after mounting the receptacle on the substrate 12 in addition to the requirement of these cover and tape.